Carb Tuning & Drivability, Need Some Guidance

[85MUSTANGTGT]

Hoping to appeal to the experts here for a bit of advice.

Over the last several years, I have been slowly trying to dial in the tune on the 347 I built and installed in my ’85 GT. I have done a lot of research, reading various forum threads and online magazine articles, but very little of it seems to focus on tuning for street applications or goes into depth on anything much other than idle mixture screws and main jets. Though with what info I have found I have been able to get my car running decently. I installed a wideband A/F ratio gauge last year which has helped me a great deal. Primarily, my focus has been on the idle and transition circuits. I’ve piddled with the primary and secondary main jets some to get them in a tolerable range, but they are still slightly on the rich side for now. Trying to get a clean idle and cruise, good throttle response, and reasonable performance.

At this point I’m seeing the following A/F ratios on idle and transition circuits:
-Idle, cold (choke closed, fast idle) – 13:1
-Idle, warm-up (choke open, normal idle speed) – 15-16:1
-Idle, fully warm – 12.5-13:1
-Transition, warm-up (steady cruise) – 14:1 climbs to 17-20:1
-Transition, fully warm (steady cruise) – 13:1

My main problem is with transition cruise during warm up driving. After accelerating to speed, with engine RPM between 1500-2000 or so, the AFR will initially settle around 14:1 then after a few seconds start getting leaner and starts misfiring. I have to keep rolling in the throttle a bit until its fully warm. With the current settings, the car runs well when fully warm. Are these AFR numbers normal? I’d like to see the warm numbers a bit leaner if possible, but worried about the cold AFR getting any leaner than it is. I know numbers aren’t necessarily everything.

From a drivability standpoint, is this normal with a carb? Have to deal with the leanness issues until its warmed up? I do let the car warm up in the driveway for a while before driving. Maybe I’m too accustomed to my newer fuel injected cars, just find it a bit irritating having let it warm up then it runs like crap for the first 10 min. of driving. As of now, this is the best the car has run since I’ve owned it. Trying to make this run as well as possible.

I’m currently running an open-element air cleaner. Would refitting the stock air cleaner w/snorkels and heat risers help with cold drivability? May take some modifying to fit with strut tower brace, though. I could see how a warmer air charge could richen up the mixture with the engine cold and the colder air charge could lean the mixture when the engine warms up, at least in theory. Not sure how much difference this would actually make. Tempted to do this whether it will help or not.

Would going to a non-air-gap manifold be a worthwhile change? Would consider this to be an absolute last resort change. I've read of some people having issues with air-gap manifolds on the street, but others not so much. Matter of opinions, I suppose.

Any other suggestions I could try to increase cold drivability? I’m running out of ideas.

Engine Setup:
-10.5:1 C/R
-AFR 185cc Heads w/ 58cc Chamber
-Cam: .526/.532 Lift, 214/222 Dur @ .050”, 110 LSA
-PP Crosswind Intake (Perf RPM Air-Gap Equiv.)
-Holley SA 670cfm Carb
-Stock Duraspark II Ignition & Distributor
-Vacuum:17-18in. Hg Idle / 21-22in. Hg Cruise / 19in. Hg OD Cruise

Current Timing Settings:
-Initial: 14 deg.
-Centrifugal Adv.: 22 deg.
-Initial + Centrifugal (Total): 36 deg.
-Vacuum Adv.: 12 deg. (on manifold vacuum)
Note: Not positive about timing curve (can’t watch tach and operate timing light by myself), but using the factory(?) light and heavy springs. Guessing it’s probably all in by 3500 or so.

Current Carb Settings:
-Floats set w/ fuel level @ bottom of sighthole
-Fuel pressure @ 4-5psi
-T-slot square (~.020” showing)
-Idle Screws: 5/8 turn out
-IFR’s: .0225P/.028S (.026P/.028S Stock)
-IAB’s: .079P/.050S (Stock)
-MAB’s: .028P/.025S (Stock)
-68 Primary Jet (65 Stock)
-72 Secondary Jet (68 Stock)
-9.5 Power Valve (6.5 Stock)
-PCVR: .035 (.055 Stock)
-.031 Acc Pump Nozzle
-Orange Pump Cam, #1 Hole
Note: PCVR’s, IFR’s, & Primary IAB’s have been drilled/tapped for set screw restrictors/bleeds.

Current Engine Compartment (for what it’s worth)


Sorry if this is a little long, trying to give as much info as possible. Will be happy to provide more details if needed.

Thanks in advance for any insight,
Thomas